As for people who live in such a technology era, we have experienced a lot of marvelous inventions which are as thousands times as the inventions before. We have get uesd to witness the new inventions released.So, I think the greatest invention must be created for common people and can improve their daily life. All the inventions invented for making more money can't desreve the name of the greatest invention. By this standard, I think the greatest invention in the history is paper. Trace to the ancient time, people needed some special materials to record imporntant events and thier thoughts to teach their later generations. People in ancient China used sliced bamboo to write down words, then used lighter material silk to replace sliced bamboo. But the price of silk was very expensive, and Confucius promoted that common people also needed to educated. In that case, some substitutes were really needed to be created. After practicing a lot of time, Cailun, the man lived in Han dynasty created paper which was very cheap for common people. you can image that if everyone could read paper books 2000 years ago, how imazing it was!